Conventionally, discharge lamps such as deuterium lamps are known. A discharge lamp disclosed in Patent Document 1 is disposed with a cathode, an anode, an aperture member, and a shield electrode in a sealed vessel filled with gas, and forms a discharge between the cathode and anode. The cathode is formed of a filament, and thermal electrons generated by conduction of electricity to the filament lead into an opening of the aperture member through an opening of the shield electrode, and are collected by the anode. In the vicinity of the opening of the aperture member, gas particles charged by thermal electrons emit light, and the emitted light is output to the outside via a sidewall of the sealed vessel.    Patent Document 1: Japanese Translation of International Application No. 2004-519077